a. Technical Field
This disclosure relates generally to fluid gauging systems and methods, including fuel-gauging systems and methods for determining the density of fuel associated with a fuel tank, such as an aircraft fuel tank.
b. Background Art
It is common to determine or estimate the density of fuel in an aircraft fuel tank in order to, among other things, determine the total fuel mass on board an airplane. With 14 C.F.R. Part 25 airplanes, the fuel quantity may be displayed in terms of mass, rather than volume, as the fuel mass does not change with temperature, and the amount of usable energy in the tanks is proportional to the mass of the fuel in the tank. Because densitometers have been traditionally expensive, heavy, and sometimes unreliable compared to other gauging components inside a fuel tank, some aircraft fuel quantity gauging systems may simply infer the density of the fuel density based on a fuel dielectric constant and/or fuel temperature. In some systems without densitometers, density determination can be the largest source of fuel gauging error.
Moreover, some conventional densitometers, which measure density as a function of the resonant frequency of a structure in contact with the fuel, include a vibrating spool. Vibrating spool type densitometers have been adopted for use in the majority of 14 C.F.R. Part 25 transports over 150 passengers. Operation of such vibrating spools and corresponding density calculations from the resulting data can be made.
It is noted that vibrating spool densitometers were initially developed for ground based petroleum applications, and were subsequently adopted for aircraft fuel gauging. Vibrating spool densitometers for aircraft are described in U.S. Pat. Nos. 4,802,360; 4,546,641; 4,495,818; and 4,215,566, all of which are hereby incorporated by reference as though fully set forth herein.
Consequently, it can be desirable to provide a highly accurate fuel quantity gauging system that can, inter alia, measure the fuel density and improve gauging accuracy.